1. Field of the Invention
The present invention relates to a throwaway insert (to be referred to as an insert) provided with a roughly circular cutting edge removably attached to a throwaway-type ball end mill (to be referred to as a ball end mill).
2. Description of the Related Art
A ball end mill is known in the prior art in which an insert, on which a roughly circular cutting edge is formed on a certain flank on a roughly plate-shaped insert body, is inserted into a groove-shaped insert mounting seat formed on the distal end of a tool body that rotates about an axis, and attached to the insert mounting seat so that the rotational locus of the roughly circular cutting edge about the axis is roughly hemispherical.
As disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 4-146015, one example of an insert used in this type of ball end mill consists is that in which, when the tool body in which the insert is attached to the insert mounting seat is viewed from the distal end in the direction of its axial rotation, the roughly circular cutting edge formed on a flank of the insert body is in the form of a convex curve that protrudes towards the front side in the direction of tool rotation.
In this insert, since the roughly circular cutting edge is twisted about the axis towards the rear side in the direction of tool rotation as it moves towards the rear end side in the axial direction, the degree of cutting by the cutting edge is satisfactory and cutting resistance is decreased.
When a roughly circular cutting edge formed on a flank of the insert body is twisted about the axis towards the rear side in the direction of tool rotation as it moves towards the rear end side in the axial direction, the thickness of the insert body at the flank on which the cutting edge is formed gradually decreases moving toward the rear end side in the axial direction. As a result, the thickness of the flank unavoidably tends to decrease on the rear end side of the insert body.
However, the thickness of the insert body as described above is not taken into consideration at all in the insert disclosed in the aforementioned publication. Moreover, since the helix angle of the cutting edge is set to an extremely large angle of 20° to 40°, on the rear end side of the insert body, the thickness of the insert body at the flank becomes excessively thin, and as a result, the rigidity of the insert body is unable to be adequately secured, thereby resulting in the possibility of being unable to carry out stable cutting processing.
In consideration of the aforementioned problems, the object of the present invention is to provide an insert and a ball end mill to which this insert is attached that allows stable cutting processing while maintaining satisfactory cutting by the cutting edge and reducing cutting resistance without lowering the rigidity of the insert body.